The present invention relates to a variable swirl siamese type intake port structure for an internal combustion engine cylinder head, and more particularly relates to such a siamesed type variable swirl intake port structure for an internal combustion engine cylinder head, which incorporates two intake valves (and thus is of the three valve type or the four valve type) and a switchover valve construction for selectively supplying intake air - fuel mixture to said two intake valves in varying proportions, and which is improved as regards air - fuel mixture swirling characteristics and volumetric efficiency in various engine operational conditions.
The present invention has been described in Japanese patent applications Ser. Nos. Showa 60-163149 (1985) and Showa 60-186886 (1985), both of which were filed by an applicant the same as the entity assigned or owed duty of assignment of the present patent application; and the present patent application hereby incorporates into itself by reference the text of said Japanese patent applications and the claims and the drawings thereof; copies are appended to the present application. Further, the present applicant wishes to attract the attention of the examining authorities to the existence of a copending patent application ser. No. Showa 56-143215, which may be considered as relevant to the examination of the present patent application.
In the prior art, there are various types of intake port structures for internal combustion engine cylinder heads, and in particular for so called siamese type cylinder heads. Such intake port structures typically are of the variable swirl siamese type, in which the siamesed intake port comprises a generally straight intake passage and a generally helical intake passage arranged in parallel with said generally straight intake passage, so that both said generally straight intake passage and also said generally helical intake passage receive supply of intake air - fuel mixture from the engine intake manifold, with a control valve selectively at least partially interrupting the flow of air - fuel mixture through said straight intake passage, so as selectively provide extra swirl for the intake air - fuel mixture being sucked into the combustion chamber of the engine, so as to improve combustibility, flame front propagation speed, and firing efficiency and thereby militate against engine knocking, thereby to allow the engine to be operated with a weaker intake air - fuel mixture than would otherwise be practicable. Such a construction typically includes a separating wall which divides between said generally straight intake passage and said generally helical intake passage. And a prior art to the present patent application, Japanese patent application Ser. No. 56-143215 (1981) which has been laid open as Japanese Patent Laying Open Publication Ser. No. 58-48715 (1983) and which was filed by an applicant the same as the applicant of the Japanese patent application of which the priority is being claimed in the present application and to whom either the present application is assigned or is owed a duty of assignment of the present application, discloses an improved siamesed type intake port structure for an internal combustion engine cylinder head which is provided with a bypass air passage through said separating wall, connecting a point on the generally straight intake passage downstream of said control valve provided therein to a vortex end wall of the generally helical intake passage.
With such an intake port structure for an internal combustion engine cylinder head, when the control valve is controlled to be in the closed state by a control system therefor, all of the air - fuel mixture sucked in by the combustion chamber of the engine is inhaled through the generally helical intake passage, and is accordingly imparted with strong swirling; this mode of operation is appropriate for when the engine is operating at low load, as during the idling engine operating condition. In this condition, because of this swirling motion, the limit to which the air - fuel mixture being supplied to the engine can be weakened without engendering deleterious effects is extended. However, at this time the resistance presented to flow of air - fuel mixture by the generally helical intake passage alone is high. On the other hand, when the control valve is controlled to be in the open state by the control system therefor, most of the air - fuel mixture sucked in by the combustion chamber of the engine is inhaled through the generally straight intake passage with only a minor proportion thereof being inhaled through the generally helical intake passage, and accordingly the inhaled air - fuel mixture as a whole is imparted with relatively weak swirling, thus accordingly causing the volumetric efficiency of the engine to be high so as to develop good engine power; this mode of operation is appropriate for when the engine is operating at high load, such as full load. At this time the resistance presented to flow of air - fuel mixture by the combination of the generally straight intake passage and the generally helical intake passage is relatively low.
There is however a problem with such an intake port structure for an internal combustion engine cylinder head, in that, when the control valve is thus controlled to be in the closed state by its control system and all of the air - fuel mixture sucked in by the combustion chamber of the engine is being inhaled through the generally helical intake passage and is accordingly being imparted with strong swirling, although the apparent flame propagation speed is improved and the weak mixture limit is extended, nevertheless because of the swirling of the air - fuel mixture in the combustion chamber the fuel therein is preferentially thrown towards the periphery of the combustion chamber by centrifugal force, and so in the radial direction of the combustion chamber there is created an air/fuel ratio gradient, with the air - fuel mixture at the center portion of the combustion chamber being weaker than the air - fuel mixture at the edge portion thereof. Accordingly, if the air/fuel ratio of the overall air - fuel mixture being supplied to the combustion chamber is near the limit in the weakness direction, then the air/fuel ratio at the center portion of the combustion chamber may become too low for good ignition, and, since in such a three valve type or four valve type internal combustion engine it is convenient and usual to locate the spark plug at the center or approximate center of the combustion chamber, this means that the air/fuel ratio of the air - fuel mixture near and around the ignition portion of said spark plug may become too low for proper ignition. For this reason, according to the conventional art, it is not practicable to push the weakening of the intake air - fuel mixture to the limit, even although good combustion chamber swirling is being provided by such a siamese type intake port structure as detailed above.
Also, as a subsidiary desideratum for such a siamese type intake port structure for such an internal combustion engine cylinder head, it is important that, especially during transient driving conditions, the fuel supply responsiveness of the engine should be as good as possible.